Process for the sensitization of photoconductors



United States Patent 3,287,123 PROCESS FOR THE SENSITIZATION OF PHOTOCONDUCTORS Helmut Hoegl, Geneva, Switzerland, assignor, by mesne assignments, to Azoplate Corporation, Murray Hill NJ.

No Di'awing. Original application July 24, 1961, Ser. No. 125,984. Divided and this application Jan. 18, 1965, Ser. No. 426,386 Claims priority, application Germany, May 29, 1959,

K 37,853; July 28, 1960, K 41,311 30 Claims. (CI. 96-15) This application is a division of copending application Serial No. 125,984, filed July 24, 1961, now abandoned, which, in turn, is a continuation-in-part of application Serial No. 30,752, filed May 23, 1960, and also now abandoned.

Electrophotographic material normally consists of a support on which there is a photoconductive substance, this coating being provided in the absence of light with an electrostatic charge. Then, the material is exposed to light behind a master, or an episcopic image is projected thereon, so that an electrostatic image is formed which corresponds to the master. This image is developed by being briefly contacted with a resin'powder, whereupon a visible image is formed which is, fixed by heating or by the action of solvents. In this way, an image of the master which is resistant to abrasion is obtained electrophotographically.

In the electrophotographic process as described an increase in the sensitivity of the photoconductive coatings has already been attempted by the addition of organic dyestufis, e.g. triphenylmethane, xanthene, phthalein, thiazine and acridine dyestuifs, to the photoconductors.

The absorption maxima of the organic photoconductors are mostly in the ultra-violet region of the spectrum. The addition of these dyestutf sensitizers achieves the result that the photoconductors become sensitive to visible light. Generally, the dyestutf sensitizers cause a displacement of the available sensitivity from the ultraviolet region to the visible region. With increased addition of dyestufi sensitizer, the sensitivity to visible light at first increases rapidly, but further additions give an increase in sensitivity which is much less than would be expected, and still further additions finally give no appreciable increase in sensitivity. The dyestulf seusitizers have the disadvantage that they color the coating considerably. In practice, the maximum achievable increase in sensitivity can seldom be utilized because then the photoconductor coatings have an intensity of color that is undesirable. Colorless or practically colorless photoconductor coatings are desired, since colored material can be employed only in special cases. If additions of dyestuii sensitizers are such as not to adversely affect the coloring of the coating for practical purposes, the sensitizing effect often does not meet the demands of general usage. Further, the dyestuii sensitizers have the disad- Vantage that they bleach out relatively quickly so that their sensitizing action tends to be lost during the storage of the electrophotographic material.

A process for the sensitization of photoconductor coatings has now been found in which organic substances, containing polarizing residues and being capable of serving as electron-acceptors in a' molecule complex, having low molecular weight, i.e. being non-resinous, being colorless or of pale color and having a melting point above room temperature, are added to the photoconductor coatings.

Substances which are primarily of interest as photoconductor coatings in accordance with the present process are those which can serve as electron donors in mole- "ice cule complexes of the donor/acceptor type (known as 1r-complex) and contain at least one aromatic or heterocyclic ring, which may be substituted. Such photoconductors include aromatic hydrocarbons such as naphthalene, anthracene, benzanthrene, chrysene, p-diphenylbenzene, diphenyl anthracene, p-terphenyl, p-quaterphenyl, sexiphenyl; heterocycles such as N-alkyl carbazole, thiodiphenylamine, oxadiazoles, e.g., 2,5-bis-(p-amin0- phenyl)-1,3,4-oxadiazole and its N-alkyl and N-acyl derivatives; triazoles such as 2,5 bis-(p-aminophenyl)- 1,3,4-triazole and its N-alkyl and N-acyl derivatives; rmidazolones and imidazolthiones, e.g., 1,3,4,5-tetraphenyl-imidazolone-2 and 1,3,4,5-tetraphenyl-imidazolthione-Z; N-aryl-pyrazolines, e.g. 1,3,5-triphenyl-pyrazoline; hydrated imidazoles, e.g., 1,3-diphenyl-tetrahydroimidazole; oxazole derivates such as 2,5-diphenyloXazole-2- p-dimethylaminoi,S-diphenyloxazole; thiazole derivatives such as 2-p-dialkylaminophenyl-methyl-benzthiazole; as also the following:

Oxazoles and imidazoles described in German patent application K 35,586 IVa/57b, filed Aug. 22, 1958. Acylhydrazones described in German patent application K 36,517 IVa/57b, filed Dec. 19, 1958.

2,2,4-triazines described in German patent application K 36,651 IVa/57b, filed Ian. 7, 1959.

Metal compounds of mercapto-benzthiazole, mercaptobenzoxazole and mercapto-benzimidazole described in German patent applicationK 37,508 IVa/57b, filed Apr..18, 1959.

Imidazoles described in German patent application K 37,435 Iva/57b, filed Apr. 9, 1959.

Triphenylamines described in German patent application K 37,436 Iva/57b, filed Apr. 9, 1959.

Furans, thiophenes and pyrroles described in German patent application K 37,423 IVa/57b, filed Apr. 8, 1959.

Amino compounds with multinuclear heterocyclic and multinuclear aromatic ring system described in Ger- 111193.511 patent application K 37,437 Iva/57b, filed Apr. 9,

Azomethines described in German patent application K 29,270 Iva/57b, filed July 4, 1956.

Molecule complexes are defined in H. A. Staabs Einfuhrung in die theoretische organische Chemie (Introduction to Theoretical Organic Chemistry), Verlag Chemie, 1959, pp. 694-707, and by L. I. Andrews, Chemical Review, vol. 54, 1954, pp. 713-777. In particular, the donor/acceptor complex (r-complexes) and "charge-transfer complexes which are formed from an electron-acceptor and an electron-donor are included. In the present'case, the photoconductors are the electrondonors and the substances here called activators -to distinguish them from the dyestuti sensitizers-are the electron-acceptors. The electron-donors have a low ionization energy and have a tendency to give up electrons. They are bases in the sense of the definition of acids and bases given by G. N. Lewis (H. A. Staab, as above, p. 600). The electron-donors primarily concerned in the present case are the photoconductors described above. These photoconductors consist of aromatic or heterocyclic systems containing a plurality of fused rings, or, alternatively, single rings having substituents which facilitate further electrophilic substitution of the aromatic ring, socalled electron-repellent substituents, as described by L. F. and M. Fieser, Lehrbuch der organischen Chemie (Textbook of Organic Chemistry), Verlag Chemie, 1954, p. 651, Table I. These are, in particular, saturated groups, e.g., alkyl groups such as methyl, ethyl, and propyl; alkoxy groups such as methoxy, ethoxy and propoxy; carbalkoxy groups such as carbmethoxy, carbethoxy and carbpropoxy; hydroxyl groups, amino groups 3 i and dialkylamino groups such as dimethylamino, diethylamino and dipropylamino.

The activators'in accordance with the invention, which are electron-acceptors, are compounds with a high'electron-afiinity and have a tendency to take up electrons.

They are acids in the sense of Lewis definition. Such properties are possessed :by substances having strongly polarizing residues or groupings such as cyano and nitro groups, halogens such as fluorine, chlorine, bromine and iodine; ketone groups, ester groups, acid. anhydride groups, acid groups such as carboxyl groups or the:

(25 C.) are. preferable, i.e. solid substances, because.

these impart a particularly long shelf life to the photoconductive coatings as a result of their 'low vapor pres sure. Substances which are rather deeply colored-such as quinones can be used, but those that are colorless or only weak in'color are preferable. Their absorption maximum should preferably be in the ultraviolet region of the spectrum, i.e. below 4,500 A. Further, the activator substances in accordance with the present process should be of lower molecular weight, i.e. between about 50 and 5000, preferably between about 100 and 1000, because with activators of lower molecular weight it is possible for reproducible results to be'obtained insofar as sensitivity is concerned. Also, the sensitivity remains constant over rather long periods, since substances of lower molecular weight, unlike those of high molecular Weight,-undergo hardly any change during storage. The' following are examples of such substances:

2-bromo-5-nitro-benzoic acid o-Chloronitrobenzene. 2-bromobenzoic acids Ohloracetophenoue. 2-chloro-toluene-4-sulphonic 2-ehlorocinnamic acid.

chloride. 4-chloro-3-nitro-11benzoic acid Mncoehloric acid. 4-chloro-2-hydroxy-heuzoic acid- Mucobromic acid. 4-chloro-1-phenol-3-sulphonic acid. Styrenedibromide. 2-chloro-3-nitro-1-to1uene-5-sul- Tetrabromo xylene.

phonic acid. 4-chloro-3-nitro-benzene-phos- B-Trichlorolactic acid nitrile.

phonic acid. Dibromosuccinic acid Triphenylchloromethaue. 2,4-dich1orobenzolc acid Tetrachlorophthalic acid. Dibromomaleic anhydride Tetrabromophthalic acid. 9,10-dibromoanthraceue Tetraiodophthalic acid. 1,5-dichlornaphthalene.-- Tetrachlorophthalic anhydride. 1,8-dichloronaphthalene Tetrabromophthalic anhydride. 2,4-diuitro-1-chlorouaphthalene--- Tetraiodophthalic anhydride. 3,4-dichloro-nitrobenzene Tettgiclhltirophthalic acid monoe y es er. 2,4-dlchloro-benzisatiu Tettzzil'lablroruophthalic acid monoe y es er. 2,cdichloro-benzaldehyde Tettgaitludgphthalic acid monoe y es er. Hexabromonaphthalic anhydride Iodoiorm. bz-l-cyanobeuzauthroue Fumaric acid dinitrile. Cyan acetic acid Tctracyanethylene. 2-cyanocinnamic acid s-Tricyauo-benzene. 1,5-dicyanonaphthalene 3,5-dinitrobenzoic acid 2,4-dinitro-1-chloronaphthalene. 3,5dinitrosalicylic acid 1,4-dinitro-naphthalene. 2,&-dinitro-1-benzoic acid. 1,5-dinitro-naphtha1ene. 2,Q-dinitro-l-toluene-B-sulfon 1,8-dinitro-naphthalene. 2,6-dil1itr0-l-phenol-4sulphoulc 2-nitrobenzoic acid.

ac 1,3-dinitro-benzene i rnitrobenzoic acid. 4,4-dinitro-biphenyl i-nitrobeuzoic acid. 3-nitro-4-methoxy-benzoic acid 3-nitro-4-ethoxy-benz0ic acid. 4-nitro-1-methyl-benzoic acid 3-nitro-2-cresol-5-sulphonic acid. c-nitro-4-methyl-1-phenol-2-su1- 5-nitrobarbituric acid.

phonic acid. 2-nitrobenzenesul hinic acid 4-nitro-acenaphthene. 3-nitro-2-hydroxy -1-henzoic acid--- 4-nltro-benzaldehyde. 2-nitro-1-phenol-4-sulphouic acid--. A-nitro-phenol. 3-nitrc-IfI-butyl-carbazole Picryl chloride. 4-nitrob1phenyl 2,4,7-trinitro-fluorenoue. Tetrauitrofluorenone. s-Triuitro-benzcne. 2,4,6-trinltro-anisole Anthraquinone 1-chloro-2-methyl-anthraquinone. AnthraquinoneZ-carboxylic acid--- Duroquinone. Anthraquinone-2-aldehyde 2,6-dichloroquinone.

1,5-diphenoxy-anthraquinone.

2,7-dinitro-anthraquinone.

Anthraqtflnone-2-sulphonic acid anilide. Anthraquinone-Zfl-disulphonit:

A acid.

Anthraquinone-2,7-disulphonic 1,5-dichloro-anthraquinoue.

acid bis-anilide. .Anthraquinone-2-sulphonic acid 1,4-dhnethyl-anthraquinone.

dimethylamide. .Aceuaphthenequinone 2,5-dich1oro-benzoquinone. Anthraquinone-z-sulphonic acid 2,3-dichloro-uaphthoquinonc-M. methylamide. Acenaphthenequinonedichloride 1,5-dichloro-anthraquinone. a Benzoquinone-l, 1-methyl+chloro-anthraquinone. 4-nitro-1-phenol-2-sulphonic acid.-- Picric acld. 1,2-benzanthraquinone 2-methylanthraquinonm Bromauil Naphthoquinone-1,2. l-chloroA-nitro-authraquinone. Naphthoquinone-1,4. Chloranil Pentacenequinone. l-chlor-anthraquinone- Tetracene-7,l2-quinone. Chrysenequinone 1,4-toluquinone.

Thymoquinone 2,5,7,lfl-tetrachloropyrenequinoue.

The quantity of the solid, non-resinous, substantially colorless electron-acceptors (activators) which is; best incorporated in the photoconductive coating to be sensii tized is easily established by simple experiments. Thea photoconductive coating containing at least one photo-.

conductor and at least one solid, non-resinous, substan tially colorless, electron-acceptor, should contain a the: photoconductor and electron-acceptor in proportions rang-.

ing from substantially less than .equal amounts to a substantial excess of the photoconductor with respect to the.

electron-acceptor.

The optimum of the proportions varies somewhat according to the substance used. Gen- 1 erally, minor amounts are used, i.e. from about. 0.1 to

ceptorin proportions ranging from substantially less than equal amounts to a substantial excess of the electroni acceptor .with respect to the .photoconductor. These,

proportions in which minor amounts of the .photocon ductor are added to the activator vary according to the substance used; however, in general, amounts from about 0.1 to about 300 moles, preferably from about 1 to,

about 50 moles photoconductor per 1000 moles activator are used. In some cases, it is also possible to use more than 300 moles: photoconductor or activator per 1000 moles activator or photoconductor, respectively, but by exceeding the above range the dark decay of the mixture usually increases, and in such cases coatings made therefrom are inferior.

Mixtures of several photoconductors-and activator substances may also be used.- Moreover, in addition to these substances,- sensitizing dyestuifs may be added.

By means of the present process, photoconductor coat-. ings can be prepared which have -a high degree of lightsensitivity, particularly in the ultra-violet region, and.

which are practically colorless. There is the further possibility of the photoconductor coatings being thereby strongly activated in the ultra-violet region and after wards being invested with a high degree of sensitivity.

to visible light by a very small addition of dyestutf sensitizer without it being necessary for so much dyestuff to be added that the coating takes on a deep color. Also, it is possible, by means of activators, for photoconductors such as naphthalene, whose initial sensitivity is very slight, to be given adequate sensitivity for the production of satisfactory images by electrophotographic processes.

Furthermore, by addition of minor amounts of. photoconductors to activators, photoconductive mixtures are A further increase in the.

The coatings are treated in other respects in accordance with the known processes of electrophotography, i.e. the photoconductor substances are used in the form of thin, coherent homogeneous coatings on a supporting material. The materials used as supports are primarily metals, such as aluminum, zinc, and copper; cellulose products, such as paper and cellulose hydrate; plastics, such as polyvinyl alcohol, polyamides, and polyurethanes. Other plastics, such as cellulose acetate and cellulose butyrate, especially in .a partially saponified form, polyesters, polycarbonates, and polyolefins, if they are covered with an electroconductive layer or if they are converted into materials which have the above-mentioned specific conductivity, e.g. by chemical treatment or by introduction of materials which render them electrically conductive, can also be used, as well as glass plates. in general, materials are suitable the specific resistance of which is less than 10 ohm-cm, preferably less than 10 ohm-cm.

If paper is used as the supporting material, it is preferably pretreated against the penetration of coating solutions, e.g., it can be treated with a solution of methyl cellulose or polyvinyl alcohol in water or with a solution of an interpolymer of acrylic acid methyl ester and acrylonitrile in a mixture of acetone and methylethyl ketone, or with solutions of polyamidesin aqueous alcohols or with dispersions of such substances.

For the preparation of the elecorophotognaphic material, the photoconductive compounds are preferably dissolved in organic solvents such as benzene, acetone, methylene chloride or ethyleneglycol monomethylether or other organic solvents or in mixtures of such solvents, and resins and the activatorsand possibly also the dyestufi' sensitizersare advantageously added thereto. These solutions are coated upon the supporting material in the normal manner, e.g., by immersion processes, painting or roller application or by spraying. The material is then heated so that the solvent will be removed.

A number of the compounds in question can be applied together to the supporting material or the compounds can be applied in association with other photoconductive substances.

Further, it is often advantageous for the photcconductor substances to be applied to the supporting ,material in association with one or more binders, e.g., resins. Resins primarily of interest as additions to the photocouductor coatings include natural resins such as balsam resins, colophony and shellac, synthetic resins such as coumarone resins and indene resins, processed natural substances such as cellulose ethers; polymers such as vinyl polymers, e.g. polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, polyvinyl acetals, polyvinyl alcohol, polyvinyl ethers, polyacrylic and polymethacrylic acid esters, isobutylene and chlorinated rubber.

If the photoconductive compounds in accordance with the invention are used in association with the resins described above, the proportion of resin to photoconductor substance can vary very greatly. Mixtures of from two parts of resin and one part of photoconductor substance to two parts of photoconductor substance and one part of resin are .to be preferred. Mixtures of the two substances in equal parts by weight are particularly favorable.

For the displacement of sensitivity from the ultra-violet to the visible range of the spectrum, dyestutf sensitizers can be used in addition to the activators. Even very small additions of sensitizer, c.g., less than 0.01 percent, give good results. In general, however, 0.01 to 5 percent, and preferably 0.1 to 3 percent of dyestuif sensitizer is added to the photoconductor coatings. The addition of larger quantities is possible but in general is not accompanied by any considerable increase in sensitivity.

Some examples are given below of dyestuff sensitizers which may be used with good results, and some with very good results. They are taken from Schultz Farbsto1f tabellen (7th edition, 1931, 1st vol.):

Triarylmethane dyestuffs such as Brilliant Green (No. 760, p. 314), Victoria Blue B (No. 822, p. 347), Methyl Violet (No. 783, p. 327), Crystal Violet (No. 785, p. 329), Acid Violet 6B (No. 831, p. 351); xanthene dyestuffs, namely rhodamines, such. as Rhodamine B (No. 864, p. 365), Rhodamine 66 (No. 866, p. 366), Rhodamine G Extra (No. 865, p. 366), Sulphorhodamine B (No. 863, p. 364) and Fast Acid Eosin G (No. 870, p. 368), as also phthaleins such as Eosin S (No.883, p. 375),

Eosin A (No. 881, p. 374), Erythrosin (N0. 886, p. 376),

Phloxin (@NO. 890, p. 378),, Bengal Rose (No. 889, p. 378), and Fluorescein (No. 880, p. 373); thiazine dyestuffs such as Methylene Blue (No. 1038, p. 449); acridine dyestuffs such as Acridine Yellow (No. 901, p. 383), Acridine Orange (No. 908, p. 387) and Trypaflavi-ne (No. 906, p. 386); quinoline dyestuffs such as Pinacyanol (No. 924, p. 396) and Cryptocyanine (No. 927, p. 397); cyanine dyestuffs, e.g., Cyanine (No. 921, p. 394) and chlorophyll.

For the production of copies with the electrocopying material, the photoconductive coating is charged by means of, for example, a corona discharge with a charging apparatus maintained at 6000-7000 volts. The elec-..

tro-copying material is then exposed to light in contact with a master. Alternatively, an episcopic or diascopic image is projected thereon. An electrostatic image corresponding to the master is thus produced on the material. This invisible image is developed bycontact with a developer consisting of carrier and toner. The carriers used may be, for example, tiny glass balls, iron powder or tiny plastic balls. The toner consists of a resin-carbon black mixture or a pigmented resin. The toner is used in a grain size of 1 to The developer may also consist of a resin or pigment suspended in a non-conductive liquid in which resins may be dissolved. The image that is made visible by development is then fixed, e.g., by heating with an infra-red radiator to 100-170 0., preferably -150 C. or by treatment with solvents such as trichloroethylene, carbon tetrachloride or ethyl alcohol, or steam. Images corresponding to the master characterized by good contrast etfect are obtained.

If transparent supporting material is used, the electrophotographic images can also be used as masters for the production of further copies on any type of light-sensitive sheets.

If translucent supports are used for photoconductive layers such as are provided by the invention, reflex images can be produced also.

The application of the activators in accordance with the present process is not restricted to electrophotographic coatings, but can extend to other devices containing photoconductors, e.g., photoelectric cells, photoresistances, sensing headsor camera tubes and electroluminescent apparatus.

The invention will be further illustrated by reference to the following specific examples:

EXAMPLE 1 A solution containing 26 parts by weight of polyvinyl acetate (e.g., Mowilith 50), 25.6 parts by weight of naphthalene, 0.0415 part by weight of 2,3,7-trinitrofluorenone and 800 parts by volume of toluene is applied by means of a coating device to an aluminum foil. After the coating has dried, direct images are produced thereon by the electrophotographic process in the following manner: the coated foil is given a negative electric charge by corona discharge, exposed behind a master to the light of a high-pressure mercury vapor lamp watts, at a distance of 30 cm.) for about 10 seconds and then dusted over with a developer.

The developer consists of tiny glass balls and a mixture of resin and carbon black which has been melted together and then finely divided. A developer of this sort consists of, e.g., 100 parts by weight of tiny glass balls (grain size: 100-400 approx.) and a toner (grain size: 20-50 7 approx). The toner is prepared by melting together 30 parts by weight of Polystyrol LG, 30 parts by weight of modified maleic acid resin (Beckacite K 105) and 3 parts by weight of Peerless Black Russ 552., The melt 8 EXAMPLE 5 A solution of 26 parts by weight ofpolyvinyl acetate,

21.6 parts by weight of 1,5-diethoxynaphthalene and 0.258 part by weight of 1,2-benzanthraquinone in 800 is then ground and screened. The finely dividefi resin parts by volume of toluene is applied to paper and the hares .to the parts of f f not struck by hght dunn" material is further processed as described in Example .1. P 'P a1 1d Pqsmve wage of the master becomes The exposure time (125-watt high-pressure'mercury vapor vislble. It 1s slightly heated and thereby fixed. lamp) is seconds If 4= 15 not added to h gfi Without the 1,2-benzanthraquinone addition, the copy descnbed abovefeven an e, of mmutes W1 0 still has considerable background after an exposure of 80 not produce an electrophotographic image. seconds EXAMPLE 2 r 7 EXAMPLE 6 26 parts i h f polyvinyl acetate, 16.6 pal-ts by -26 parts. by weight of polyvinyl acetate, 17.8 parts weight of fluorene and 0.3602 part by weight of tetranitro- 15 I by welgiht of PPeDanthTefle and 9- P by Welght of fluorenone are dissolved in 800 parts by volume of toluchloraml are dissolved f g i 11 300 parts by volume ene. This solution is applied to an aluminum foil and of toluenesolutlQIl 15 ppli to a superficially further procedure is as described in Example 1., Expo-' Toughaned ammmum 9 P then material 15 Sure time if a 125mm higbpressure mercury vapor lamp thenprocessed as described in Example 1. If the mateis used is 10 seconds.- Y e 7 2O nal 1s exposed to a l-watt high-pressure mercury vapor Without the tetranitrofiuorenone addition, the images lamp an eXPOSuIQOf secronds Elves an Image free obtained even after an exposure of two minutes are not backgrqund f l fish contrast Whereas Wlthout the free of background, Le, the exposed pal-ts are not f ll chloranil addition there is heavy background even after discharged and therefore retain a certain amount of dean exposure of one mmuteP veloper. 25 EXAMPLE 7 1 EXAMPLE 3 A solution containing 26 partsvby weight of polyvinyl A solution of 26 parts byweight of polyvinyl acetate, acetate, 24. 4 parts by weight of o-dianisidine and 0.0256 17.8 parts by weight of anthracene and 0.3357 part by part by Weight of dibromomaleic'anhydride in 800 parts weight of hexabromonaphthalic anhydride in 800 parts by volume of toluene is applied to an aluminum foil and by volume of toluene is applied to aluminum and further the material is further. processed as. described in Exam? procedure is as described in Example 1. With a 125-watt pie 1. The exposure time (125,-watt high-pressure .merhigh-pressure mercury vapor lamp, the exposure time is cury vapor lamp) is 2 seconds. Without the dibromo- 4 d maleic anhydride addition, it is 10 seconds.

TABLE A No. A B C D E 1 Pl inl ttyIO t.1 s 12 :17. y we a 6 g 3 Anthraquinone, 0.08 30 19 (ca) 3 dn 7 8 'Anthraquinone, 0.17 20 sec. (1)). 4 rln 8 Anthraquinone, 0 25 20 see. (b). 5 dn- 8 see. (b). 6. dn 8 60 see. (b). 7- 8 60 see. (b). 3 (in 8 0. 030 90 see. (b). 9 dn 8 0.050 90sec. (b). 10 r1n 8 Anthraqumone, 0.17 0. 001 20 see. (b). 11 d0 8 rln 0.010 20sec. (b). do 8 --dn 0. 5o 20 see. .(b). 13 dn 8 240 see. (a). dn 8 Anthraqumonc, 0 180 see. (a). Cyclized rubber, 10 parts (2) 8 240 see. (a). ,do 8 Anthraquinone, 0.25 30 se (a). Aiterchlorlnatedpolyvinylehlorlde, 7 parts (3) 8 10 see. (a) Polyvinylchloride, aiterehlorinated, 7parts (3). 8 Anthraquinonc, 0.25 part. 3 see. (a) Maleic acid resin, 10 parts (4) 8 240 see. (a) dn 8 Anthraqumone, 0.25 part. 60 see. (a) Chlorinated rubber, 10 parts (5) 8 20 see. (a) d0 8 Anthraquinone, 0.25 part 10 see. (a) Chlorinated rubber, 10 parts (6) 8 20 see. (a) rin 8 Anthraquinone, 0.25 10 sec. (3) 25 dn 8 1,2-beuzanthraquinone, 0.31 part 1-1 5 se (a) 2(; (ln 8 Hcxabromonaphthalic anhydride, 080 part. 1-1 5 ec, 27 do 8 2,t,5,7-tetranitrofiuorenone, 043 part 1.5 see. (a). 23 dn 8 D1bromomale1c anhydride, 0.30 part 4-6 see, an 8 Nitroterephthalic aciddimethylester, 0.28 6-8 see. (a).

B1 30 dn 8 'I tracyano ethylene, 0.15 part 46 see. 31 rin 8 1,3,5-trlnitrobenzene, 0.25 part 1.5-2 see. a),

image obtained after an exposure of 1 minute is not free of background.

Explanations on Table A volume of toluene.

Column B: Quantity of the photoconductorexamples, the same amount of pyrene was used.

In all Column C: Quantity of the activator used.

damine B extra).

Column E: Time of exposure, using:

crescenta) Column D: Quantity of dyestutf sensitizerused (Rho- (a) a 250 watt photographic lamp (Philips Photo- (b) a customary watt incandescent lamp.

9 The tests were carried through under the same experimental conditions, with the exception of the variations stated in the table.

(1) The polyvinyl acetate used was the product commercially available under the registered trademark M-owilith C.

(2) The cyclized rubber used was the product commercially available under the registered trademark Pliolite S-SD.

(3) The afterchlorinated polyvinylchloride used was the product commercially available under the registered trademark Rhenoflex.

(4) The maleic acid resin used was the product commercially available under the designation Alrosat."

(5) The chlorinated rubber used in Table A, col. A, under N0. 21 (5) was the product commercially available under the registered trademark Parlon S-5 cps.

(6) The chlorinated rubber used in Table A, col. A, under N0. 23 (6) was a product commercially available under the registered trademark Pergut 5-40.

The following Table B shows further examples of various photoconductors which were activated, and the reduction in exposure time caused by the activators:

TABLE B Chloranil. Hexabromonaphthalic anhydride 13.6 hydroquinonedimethylether.

2,4,5,7-tetranitrotluorenone Heiregromonapbthalie anhy 25.6 naphthalene- 26 21.6 1,5-diethoxynaphthalene.

15.4 acenaphthene mmxwmxxxxx 9 Ch Cl Q,

15.2 aeenaphthylene* 15.4 diphenyl Tetrachlorophthalie anh Picrylchloride 2,4.5,7-tetranitrofluorenone- Chloranil 24.4 o-dianisidine 1,2-benzanthraquiuone Tetrachlorophthalic anhydridefln Hexabromonaphthalie anhydride. Picrylchloride Chloranil 1,2-benzantl1raquinone Hexabrornonaphthalic anhydride. Picrylchloride 3,5-dinitrosalicylic acid- 1,2-benzanthraquinone-.- Dibromomaleic anhydride. Tetrachlorophtbalic anhydride 2,4,5,7-tetranitrofluorenone Benzoquinone- Chlorauil 3,5-dinitrosalicylic acid- 1,2-benzanthraquinone. Tetrachlorophthalie anhydr1de Hexabromouaphthalic anhydride Picrylehloride 2,4,5,7-tetranitrofluorenone, Benzoquinone hlor 2,4,5,7-tetranitrofluorenone- 1,4-beuz0quinone Chloranil- 3,5-dinitrosalicylic acid- 1,2-benzanthraquinone. Dibromomalele acid anhydr Tetraeblorophthalic anhydrida--. Hexabromonaphthalie anhydride Picrylehloride 2,4,5,7-tetranitrofluorenon 12benzanthr5quinone- Dibromomaleic anhydri Tetrachlorophthalie anhydr Hexabromonaphthalic anhydride Pierylchlortde 2,4,5,7-tetranitrofiuorenone 16.6 fluorene 17 .8 anthracene 22.8 clu'ysene 52 16.9 diphenylamine 26.9 2,2 -dlnaphthylamine 17.8 phenanthrene arenaexam:xxxxxxxgxxxmzzzsxxxsxuxxms TABLE BC0ntinued A B C 16.7 earbazole 19.9 thiodiphenylamine.--

25.48 2,4-bis(4-diethylaminopheuyl)-1,3,4- oxadiazole.

18.2 2,4-bis-(4-diethylaminopheuyD-LBA- triazole.

Explanations on Table B The table describes a series of experiments carried through for improving the photoconductivity of organic substances by adding activators.

In Column A the quantity and nature of the substance used is stated. The substances marked with a yielded no electrophotographic images even after. an exposure time of several minutes.

In Column B the quantity of the binder used is stated. In all of the cases, polyvinyl acetate having a K-value of 50 was used. .Binder, photoconductive substance, and

activator were dissolvedin toluene, coated onto an aluminum foil, and dried.

In Column C the substance used as activator is stated. In all of the cases 1 mol of the activator stated under C was used per moles of the substance stated under A.

In Column D the reduced time of exposure is stated which is required to produce images equal in quality to those produced without the addition of an activator. In those cases where a prolonged exposure of the photoconductor yielded not even a weak image (marked with a the calculation of the reduced time of exposure was based on the longest exposure used for the unactivated photoconcluctor substance.

Alternatively, the increase in sensibility obtained by the addition of activating substances may be taken from a comparison of the degrees of blackening obtained with the activated photoconductive layer and with the unactivated photoconductive layer, under the same customary step wedge (e.g. Kodak No. 2 density strip with color patches).

EXAMPLE 8 A solution containing 20 parts by weight of afterchlorinated polyvinyl chloride with a content of chlorine from 61.7 to 62.3 percent and K-value from 59 to 62, 18.01 parts by weight of 2,4,5,7-tetranitrofluorenone and 0.216 part by weight of 1,5-diethoxynaphthalene dissolved in a mixture of 450 parts by volume toluene and parts by volume butanone is applied to an aluminum foil. The subsequent procedure is that described in Example 1. The exposure time, with a 100 Watt incandescent lamp at a distance of 30 centimeters is 2 seconds.

Without the addition of 1,5-diethoxynaphthalene the exposure time is about 40 seconds.

' 11 In the following table, the exposure times are given, which were obtained when using other photoconductors instead of the 1,5-diethoxynaphthalene.

Exposure time,

uene and 150 parts by volume of butanone is applied to an aluminum foil and the material is further processed as described in Example 1. The exposure time (125 watt high pressure mercury vapor lamp at a distance of 30 centimeters) is seconds. Without the addition of the benzidine activator, even after an exposure time of 4 minutes, no electrophotographic image could be obtained.

In the following table, the exposure times are given which were obtained when using photoconductors other than benzidine.

Exposure time EXAMPLE 1 1 A solution containing 6.2 parts by weight of afterchlorinated polyvinyl chloride, 3.94 parts by weight of 1,5-dichloronaphthalene and 0.145 part by weight of 2,5-bis- (4'-diethylaminophenyl)-1,3,4-oxdiazole in a mixture of 135 parts by volume of toluene and 45 parts by volume of butanone is applied to a paper base and is further processed as described in Example 1. The exposure time (125 watt high pressure mercury vapor lamp at a distance of centimeters) is 10 seconds. Without the addition of the oxdiazole compound, even after an exposure time of seconds, no image could be obtained. When the oxdiazole compound is replaced by 0.120 part by weight of onds.

EXAMPLE 12 I To a solution containing 28.6 parts by weight of tetra- Photoconductors (Parts by weight): (seconds) 5 chlorophthalic acid anhydride and 20 parts by weight of AcenaPhthene (0154) 15 afterchlorinated polyvinyl chloride in a mixture of 150 Nfthylcarbazole 0195) 15 parts by volume of butanone and 450 parts by volume 2.2'dmaphfl.1y1amme (0270) 15 of toluene, X parts by weight of photoconductor and Diphenylamme. (0170) 15 Y parts by weight of dyestufi sensitizer are added. In the Dlphenyleneoxlde (0'170) 2O 10 following table, the amounts of the photoconductor and Indole (0'120) 10 sensitizer are given together with the corresponding ex-. PYrene (0'200) 12 posure times. It is advantageous to dissolve the dyestutf (01110) "7 5 sensitizer .in a small amount of ethyleneglycol mono-- 2:5'b1s'(4"d1ethylammopheny1)1,3,4 Oxdlazole methylether before adding it to the solution. ,The latter (0365 1 15 is applied to a paper base material and further processed P1YN'vm y1carbaZ1e (0193) 6 as described in Example 1. The light source u ed Phfinoxathme (0200) 6 throughout was a l25-watt high pressure mercury va or EXAMPLE 9 lanltp and the distajnce 13%1W6B11 this lamp and the materia ex ose was a out centimeters.

. A solution of 12 parts by weight of chlorinated rubber 20 p (Pergut S-40), 5.04 parts by weight of 1,3-dinitrobenzene and 0.106 part by weight of anthracene in 150 parts by volume of toluenc is applied to a papcr foil and the PhotoeonductorX parts Dyestufl Sensitizer Y Exposure material is further processed as described in Example 1. by Weight Parts by weight 7 Time The exposure time (125 watt high pressurehrmercurydrga- 25 (semnds) or lam is 20 seconds. Without the an acene a i- Eon, ev ri after an exposure time of secondlsl, ony g;] livp w a ii ii 011.20g

traces of an image were obtained. This means t at t e 0.30 Rho am a extra 2-3 exposed parts of the coating were not discharged and 30 j, f f i 3i ff fi None 5 therefore still attracted developer. I flfi fi -fgfi t hyl ni o- None 4 i In the following table the exposure times are given, 5 35.. x m0 0.30 RhodamlneB extra 1 z which were obtained, when using other photoconductors 53-" 3-3;; gi g g g z i -n g instead of the 1,3-dinitrobenzene. 011.- firitsgallviglet -1": g 5

Exposure time e 17 lle Photoconductors (p y (seconds) 35 153 Z.Y?.I ."."f. fi...11 hiiifi fff iffffffffffiil 23 2,2'-,dinaphthylamine (0.180) g 20- 2,5-bis-(4-diethylaminophenyl)-1,3,4 oxdiazole EXAMPLE 10 EXAMPLE 13 A solution containing 20 parts by weight of the after- A solution is prepared, containing 57.2 .parts by weight chlorinated polyvinyl chloride mentioned in Example 8, of tetrachlorophthalic acid ,anhydride and 65 parts by 21.02 parts by weight of benzile and 0.370 part by weight Weight of afterchlorinated polyvinyl chloride in 700 parts of benzidine in a mixture of 450 parts by volume of tol- 45 by volume toluene and suflicient butanone is added to make up 1000 parts by volume. i To 50 parts by volume of the resulting stock solution, one of the photoconduc-' tors listed below is added, and the solution is applied to an aluminum foil and further processed as described in Example 1. In the following table, the added photoconductors are indicated, and the corresponding exposure times are given. As the light source, a -watt high pressure mercury vapor lamp in a distance of about. 30 centimeters from the exposed material was usedin. all instances.

1 Image with heavy background,

Exposure time 1 Photoconductor (parts by weight)- Exposure time Continued (seconds) Phenanthrene (0.089) 60 Phenoxathin (0.100) 10 Stilbene (0.090) 30 2,3,5-triphenylpyrrole (0.153) 10 1,1'-dinaphthy1amine (0.134) 30 1,2'-dinaphthylamine (0.134) 30 4'-tolyl-1-naphthylamine (0.116) 60 2-phenylindole (0.096) 60 Acenaphthene (0.077) 60 Diphenyl (0.077) 120 N-methyldiphenylamine (0.091) 30 4-hydroxy-diphenylamine (0.092) 30 Phlorglucinediethyl ether (0.091) 120 EXAMPLE 14 57.2 parts by weight of tetrachlorophthalic acid anhydride and 65 parts by weight of polyvinyl acetate are dissolved in sufiicient toluene to make up 1000 parts by volume. To 50 parts by volume of this stock solution, one of the photoconductors listed below is added and the coating solution is applied to an aluminum foil and further processed as described in Example 1. The light source and the distance of the light source from the exposed material were the same as in the foregoingexample.

Exposure time Photoconductor (parts by weight): (seconds) None 60 Naphthalene (0.064) 10 Hydroquinonedimethyl ether (0.069) 2 N-ethylcarbazole (0.097) 2 Anthracene (0.089) 2 Carbazole (0.081) 3 Chrysene (0.114) 4 Pyrene (0.101) 10 o-Dianisidine (0.122) 3 1,5-diethoxynaphthalene (0.101) 4 2,6-dimethyl-naphthalene (0.078) 10 Hexamethylbenzene (0.081) 10 2,2'-dinaphthylamine (0.134) 4 Diphenylamine (0.084) 2 Diphenyleneoxide (0.084) 10 Indole (0.058) 4 Fluorene (0.083) 4 Stilbene (0.090) 4 EXAMPLE 15 Photoconductor (parts by weight): (seconds) None 1 60 N-ethylcarbazole (0.10) 5 Anthracene (0.09) Chrysene (0.114) Pyrene (0.10) 10 2,2'-dinaphthylarnine (0.134) 10 2,3,5-triphenylpyrrole (0.153) 10 No image obtained,

EXAMPLE 16 49.2 parts by weight of chloranil and 5 6 parts by weight of afterchlorinated polyvinyl chloride are dissolved in a mixture of 1170 parts by volume of toluene and parts by volume of butanone. The resulting solution is filled up to 2000 parts by volume with chlorobenzene. To 100 parts by volume of this stock solution, one of the photoconductors listed in the following table is added; the coating' solution is applied to an aluminum foil and further processed as described in Example 1. The light source and the distance of the light source were the same as in Example 13.

Exposure time EXAMPLE 17 10.6 parts by weight of Z-acetyl fiuorene and 12 parts by weight of afterchlorinated polyvinyl chloride are dissolved in parts of toluene and sufiicient butanol to make up 250 parts by volume of solution. To 50 parts by volume of this stock solution, one of the photoconductors of the following table is added. The solution is applied to an aluminum foil and further processed as described in Example 1. The light source and the distance of the light source were the same as in Example 13.

Exposure time Photoconductor (parts by weight): (seconds) None 1 180 o-Dianisidine (0.120) 30 2,5 -bis- (4'-diethy1arninophenyl) -1,3,4-oxdiazole 1 No image obtained.

EXAMPLE 18 44 parts by weight of 9 acetyl-anthracene and 48 parts by weight of afterchlorinated polyvinyl chloride are dissolved in 700 parts by volume of solution. To 50 parts by volume of the resulting stock solution, one of the photoconductors of the following table is added. This solution is applied to an aluminum foil andfurther procr essed as described in Example 1. The light source and the distance thereof was the same as in Example 13.

Exposure time Photoconductor (parts by weight): (seconds) None 1 180 Hydroquinonedimethyl ether (0.069) 30 N-ethyl carbazole (0.097) 60 Anthracene (0.089) 60 Hexamethylbenzene (0.081) 30 1 Image with heavy background.

EXAMPLE 19 46.2 parts by weight of pyrene-B-aldehyde and 50 parts by weight of afterchlorinated polyvinyl chloride are dissolved in 670 parts by volume of toluene and suflicient butanol to make up 1000 parts by volume of solution. To 50 parts by volume of the resulting stock solution one of the photoconductors of the following table is added. The solution is applied to an aluminum foil and further processed as described in Example 1. The light source 15 and the distance of the light source were the same as in Example 13.

Exposure time 13.1 parts by weight of 1,4,5-trinitronaphthalene and 15 parts by weight of afterchlorinated polyvinyl chloride were dissolved in 180 parts by volume of toluene and sufficient butanone to make up 250 parts by volume. To 50 parts of the resulting stock solution, one of the photoconductors of the following table is added in the amount indicated. This solution is applied to an aluminum foil and further processed as described in Example 1. The light source and the distance, thereof were the same as in Example 13.

Exposure time Photoconductor (parts by weight): (seconds) None 7 1 180 N-ethylcarbazole (0.10) 30 Anthracene (0.09) 30 o-Dianisidine (0.12) 10 2,5-bis-(4'-diethylaminophenyl)-1,3,4-oxdiazole 1 Image with heavy background.

It will be obvious to those skilled in the art that many modifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications.

Whatis claimed is:

1. A sensitized photoconductive layer comprising at least one solid, non-resinous, substantially colorless electron-acceptor, and a compound having the formula in which R and R are selected from the group Consisting of fused ring arylene groups, alkylamino substitutedfused ring arylene groups, andamino substituted fused ring arylene groups, each of R and R containing not in excess of two fused rings, and R is selected from the group consistingof and radicals.

2. A sensitized photoconductive layer comprising at least one solid, non-resinous, substantially colorless electron-acceptor, and a compound having the formula in which R and R are selected from the group consisting of fused ring arylene groups, alkylamino substituted fused ring. arylene groups, and amino substituted fused ring arylene groups, each of R and R containing not 16 in excess of two fused rings, and R is selected from the group consisting of H OH =N-, =C- and =C- radicals; the layer containing the photoconductor and the electron-acceptor in proportions ranging from substantially less than equal amounts to a substantial excess 7 of the photoconductor with respect to the electron-ac ceptor and from' substantially less than equal amounts to a substantial excess of the electron-acceptor .with

respect to the photoconductor.

3. A'sensitized photoconductive layer comprising at, least one solid, non-resinous, substantially colorless elec- I tron-acceptor, and a compound having the formula in which R and R are selected from the group consisting of fused ring arylene groups, alkylamino substituted fused ring arylene groups, and amino substitutedfused ring arylene groups, each-of R and R containing not in excess of two fused rings, and R is selected from the group consisting of and =C radicals; in proportions rangingfrom about 0.1 to about 300 moles of the electron-acceptor per 1000 moles of photoconductor.

4. A sensitized photoconductive layer comprising at least one solid, non-resinous, substantially colorless elec:

tron-acceptor, and a compound having the formula in which R and R are selected from the group consist ing of fused ring arylene groups, alkylamino substituted fused ring arylene groups,,and amino substitutedfused ring arylene groups, each of R and R containing not in excess of two fused rings, and R is selected from the group consisting of H OH radicals; in proportions ranging from about 0.1 to about 300 moles of the photoconductor per 1000 moles of the electron-acceptor.

5. A sensitized photoconductive layer comprising'at least one solid, non-resinous, substantially colorless electron-acceptor, and a compound having the formula in which R and R are selected from the group consist ing of fused ring arylene groups, alkylamino substituted fused ring arylene groups, and .amino substituted fused.

ring arylene groups, eachof R and R containing not in excess of two fused rings, and R is selected from the group consisting of radicals; in proportions ranging from about 1 to about 50 moles of the electron-acceptor per 1000 moles of the photoconductor.

in which R and R are selected from the group consisting of fused ring arylene groups, alkylamino substituted fused ring arylene groups, and amino substituted fused ring arylene groups, each of R and R containing not' in excess of two fused rings, and R is selected from 'the group consisting of radicals; in proportions ranging from about 1 to about 50 moles of the photoconductor per 1000 moles of the electron-acceptor.

7. A layer according to claim 1 in which the electronacceptor is 2,4,7-trinitrofluorenone.

8. A layer according to claim 1 in which the electronaeceptor is tetranitrofluorenone.

9. A layer according to claim 1 in which the electronacceptor is hexa'bromonaphthalic anhydride.

10. A layer according to claim 1 in which the electronacceptor is tetrachlorophthalic anhydride.

11. A layer according to claim 1 in which the electronacceptor is 1,2- beuzanthraquinone.

12. A layer according to claim 1 in which the electronacceptor is chloranil.

13. A layer according .to claim 1 in which the electronacceptor is dibromomaleic anhydride.

14. A layer according to claim 1 including a resin.

15. A layer according to claim 1 including a dyestuff sensitizer.

16. A photographic reproduction process which comprises exposing an electrostatically charged, supported, photoconductive insulating layer to light under a master and developing the resulting image with an electroscopic material, the photoconductive layer comprising at least one solid, non-resinous, substantially colorless electronacceptor and a compound having the formula in which R and R are selected from the group consisting of fused ring arylene groups, alkylamino substituted fused ring arylene groups, and amino substituted fused ring arylene groups, each of R and R containing not in excess of two fused rings, and R is selected from the group consisting of 17. A photographic reproduction process which comprises exposing an electrostatically charged, supported, photoconductive insulating layer to light under a master and developing the resulting image with an electroscopic material, the photoconductive layer comprising at least one solid, non-resinous, substantially colorless electronacceptor and a compound having the formula in which R and R are selected from the group consisting of fused ring arylene groups, alkylamino substituted group consisting of fused ring arylene groups, and amino substituted fused ring arylene groups, each of R and R containing not in excess of two fused rings, and R is selected from the =N :c radicals; the layer containing the photoconductor and the electron-acceptor in proportions ranging from substantially less than equal amounts to a substantial excess of the photoconductor with respect to the electronracceptor and .and from substantially less than equal amounts to a substantial excess of the electron-acceptor with respect to the photoconductor.

18. A photographic reproduction process which c'omprises exposing an electrostatically charged, supported, photoconductive insulating layer to light under a master and developing the resulting image with an electroscopic material, thephotoconductive layer comprising at least one solid, nonresinous, substantially colorless electronacceptor and a compound having the formula in which R and R are selected from the group consisting of fused ring arylene groups, alkylamino substituted fused ring arylene groups, and amino substituted fused ring arylene groups, each of R and R containing not in excess of two fused rings, and R is selected from the group consisting of and =0- in which R and R are selected from the group consisting of fused ring arylene groups, alkylamino substituted fused ring arylene groups, and amino substituted fused ring arylene groups, each of R and R containing not in excess of two fused rings, and R is selected from the group consisting of and =0- radicals; in proportions ranging from about 0.1 to about 300 moles of the photoconductor per 1000 moles of the electron-acceptor.

20. A photographic reproduction process which comprises exposing an electrostatically charged, supported, photoconductive insulating layer to light under a master and developing the resulting image with an electroscopic material, the photoconductive layer comprising at least one solid, nonresinous, substantially colorless electronacceptor and a compound having the formula in which Rand R are selected from the group consisting of fused ring arylene groups, alkylamino subs'titutedfused ring arylene groups, and amino substituted fused ring arylene groups, each of R andR containing not in excess of two fused rings, and R is selected from the group, consisting of 1 1 =N, =o-- and =o radicals; in proportions ranging from about 1 to about 50 moles of the. electron-acceptor per 1000 moles of the photoconductor.

21.'A photographic reproduction processwhich comprises exposing an electrostatically charged, supported, photoconductive insulating layer to light under a master and developing the resulting image with an electroscopic material, the photoconductive layer comprising at least one solid, nonresinous, substantially colorless electronacceptor and a compound havingtthe formula e lectronacceptor is 2,4,7-trinitrofluorenone.

23. A process according to claim'16 in which the electron-acceptor is tetranitrofluorenone.

24. A process according to claim 16 in which the electron-acceptor is hexabromonaphthalic anhydride.-

25. A process according to claim 16 in which the electron-acceptor is, tetrachlorophthalic anhydride.

26. A process according -,to claim 16 in which the; electron-acceptor is 1,2-benzanthraquinone- 27.A' process according to claim 16, :in; which the electron-acceptor is chloranil.

28. A' process according to claim .16 in which the 1 electron-acceptor is dibromomaleic anhydride.

" 29. A process according to claim 16 in which the layer 1 includes a resin.

30. A process according to claim 16 in which'the layer:

includes a dyestutf sensitizer.

References Cited by the Examiner UNIT STATES PATENTS 3,037,861 "6 /1962 Hoegl etal 96-1 3,113,022 12/1963. Cassiers et a1. 96-1 3,155,503 11/1964 Cassiers et a1. 961

OTHER REFERENCES Andrews, Chemical Reviews, 54: 713-777, October Czekalla et al.: Chemical Abstracts 52: 4317b (1957).

' Schneider and Compton et al.: Journal of Chemical Physics, vol. 358, 1075-1076 '(1965).

NORMAN G IQRCI-IIN, Primary Examiner.

C. E. VAN HORN, Assistant Examiner.

22. A process according to claim .16 in which the, 

1. A SENSITIZED PHOTOCONDUCTIVE LAYER COMPRISING AT LEAST ONE SOLID, NON-RESINOUS, SUBSTANTIALLY COLORLESS ELECTRON-ACCEPTOR, AND A COMPOUND HAVING THE FORMULA 